It amazes me how little White actresses need to accomplish to land a Vogue cover compared to their Black counterparts. Pretty much every Black actress or singer who's gotten a Vogue cover has had an Oscar nomination, an Oscar win or a Grammy accompanied by global success. That Blake's biggest achievement is a stint on Gossip Girls speaks volumes. I mean she has never gotten any sort of nomination for her acting-- no Emmy, no golden globe, not even a MTV movie award.
I'm sorry but I HATE when people make this argument against Anna because it's more a problem with Hollywood than Vogue. What "deserving" black actress of the moment hasn't gotten a cover yet? I can think of only Kerry Washington( whom I'm sure will get one) and Zoe Saldana. Anna has shown time and again her willingness to put black celebrities on the cover and has often thought outside the Hollywood box since she doesn't really get enough options from them. Oprah, Michelle Obama, hell even Marion jones and Lebron James and like you said the minute a black actress does pass that Alist threshold she's almost guaranteed a cover. Halle even landed September and lupita got hers mere months after her oscar.